From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 1/5] Add a global synchronization point for pvclock
Date: Mon, 19 Apr 2010 12:39:05 +0200
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Cc: Glauber Costa <glommer@redhat.com>, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org, avi@redhat.com,
	Marcelo Tosatti <mtosatti@redhat.com>,
	Zachary Amsden <zamsden@redhat.com>
To: Jeremy Fitzhardinge <jeremy@goop.org>
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On Fri, 2010-04-16 at 13:36 -0700, Jeremy Fitzhardinge wrote:
> > +     do {
> > +             last = last_value;
> >   
> Does this need a barrier() to prevent the compiler from re-reading
> last_value for the subsequent lines?  Otherwise "(ret < last)" and
> "return last" could execute with different values for "last".
> 
ACCESS_ONCE() is your friend.